Projection systems are widely used in training, sales, and business environments. Referring to FIG. 1, a projection system 100 includes a projector 102 positioned on a horizontal surface 104. The surface 104 is typically a desk or tabletop. An elevator 120 protrudes from the bottom sides of the projector 102 creating an angle 110 between the surface 104 and the projector 102. Only one elevator 120 is visible in FIG. 1 although a person of reasonable skill in the art should understand that a plurality of elevators 120 might be employed in the system 100. Likewise, a person of reasonable skill in the art should recognize that the projector 102 refers to any system capable of projecting any of a variety of still or moving images, e.g., projection televisions, multimedia projectors, computer displays, and the like.
The angle 110 varies depending on the position of the elevator 120. The elevator 120 tilts the projector 102's position relative to the surface 104 such that projected image 122 moves up or down on a projection surface 114, increasing or decreasing the angle 110. The projection surface 114 might be a wall, screen, or any other surface capable of displaying a projected image 122.
The projector 102 manipulates (undistorted) image data 108 it receives from a personal computer 106. A person of reasonable skill in the art should recognize that the projector 102 might receive different types of image signals, e.g., digital or analog signals, from any of a variety of input devices including the personal computer 106. The image data 108 represents still, partial, or full motion images of the type rendered by any of a variety of input devices including the personal computer 106.
The projector 102 casts the image data 108 onto the projection surface 114. The resulting projected image 122 centers about a projection axis 116. An angle 112 exists between the projection axis 116 and the projection surface 114. The angle 112 changes responsive to the angle 110 and the horizontal position of the projector 102 on the desk or tabletop 104.
The projected image 122 is substantially undistorted—e.g., substantially rectangular in appearance—if the projection axis 116 is perpendicular to the projection surface 114. That is, the image 122 is undistorted if the angle 112 is 90 degrees. The projected image 122, however, distorts if the projection axis 116 is not perpendicular to the projection surface 114. This distortion is termed keystone distortion (or keystoning) because the image will appear wider at the top than at the bottom as shown in the image 122.
There are well known ways of correcting keystone distortion. The elevator 120 might, for example, be coupled to optics encased in the projector 102 that compensate for keystone distortion. The optics, however, are costly and prone to dust collecting that results in obscured projected images.
Signal processing circuits are often used, for example, to oppositely distort the image data 108 to thereby compensate for keystone distortion prior to projecting the image 122. But these circuits require floating point processes that exceed real time system capability.
The projector 102 might include gauges 124 used to manually adjust the projected image 122 to eliminate or minimize keystone distortion. The manual adjustments tend to move the projected image 122 out of the projection surface 114. And the manual adjustments, unfortunately, are time consuming, cumbersome, and generally an unwelcome set up complication.
Accordingly, a need remains for an automatic keystone correction system and method.